The present invention is directed to semi-rigid polyurethane foams having a density of 90 to 180 kg/m3 and a compressive strength of 20 to 95 kPa and to processes for their production and use.
Semi-rigid polyurethane foams are known and have been extensively described (Kunststoffhandbuch, volume 7, “Polyurethanes”, Carl Hanser Publishers Munich, Vienna, 3rd edition, 1993, chapter 5.4, and DE-A 10 2005 011 572). They are produced by reacting polyisocyanates with compounds having two or more isocyanate-reactive hydrogen atoms. These foams are particularly useful in the interior of motor vehicles for making instrument panels, door side parts, center consoles, arm rests and door rests. Semi-rigid polyurethane foams are frequently used in the form of so-called composite elements. Composite elements are made up of self-supporting films or sheets which are usually made of polyurethane or PVC and a backing, which is usually made of polycarbonate/ABS or fiberglass-reinforced polypropylene that are back-foamed with semi-rigid polyurethane foams.
Polyurethane foams having very good mechanical properties may be obtained by selection of suitable reaction components and reaction component mixing ratios. HCFC blowing agents are not used wherever possible for ecological reasons. Water is frequently used as an alternative blowing agent. The use of water as the blowing agent has disadvantages as well as advantages. Water-blown foams usually have worse mechanical properties than foams produced with an HCFC blowing agent. In an effort to remedy these defects and to obtain equivalent or improved mechanical properties, the isocyanate-reactive or polyol component of the foams has been extensively optimized.
The use of o-TDA-based polyalkylene oxides to produce rigid polyurethane foams is well known and has been extensively described. In the rigid foams produced with o-TDA initiated polyether polyols, the monomers typically bond predominantly via urethane groups, particularly with secondary hydroxyl functions, and crosslink via the functionality of the polyether polyols and polyisocyanates.
In contrast, semi-rigid polyurethane foams are obtained by reacting high molecular weight, preferably polyester polyols and/or polyether polyols and optionally crosslinking and/or chain-extending agents with organic and/or modified organic polyisocyanates. In these semi-rigid foams, the monomers typically bond predominantly via polyol and isocyanate groups and less via urethane groups and particularly with primary hydroxyl functions. The degree of crosslinking is low, and the average functionality of the isocyanate-reactive components is normally below three.
Polyalkylene oxides produced from 22-27 wt % of diaminotoluene and 73-78 wt % of alkylene oxides are widely used as components in rigid polyurethane foams (U.S. Pat. No. 5,547,998), flexible SRIM articles (GB-A 2308373 and CA 2157829) and sprayable elastomers. Typical rigid foams contain 2-3 kg/m3 of integrated diaminotoluene. Polyols having smaller fractions of diaminotoluene in the molecule are rarer. EP-A 1138709 describes polyols having 5-14 wt % of diaminotoluene in the polyalkylene oxide molecule. WO 2006/037540 describes rigid foams based on mixtures of diaminotoluene-based polyols having various chain lengths.
EP-A 671425 describes the production of high-resilience flame-retardant flexible foams (compressive strength<9 kPa at 40% compression) having densities of 30-60 kg/m3. The polyether polyols used to produce these foams are based on only 2-3 wt % to 12 wt % of diaminotoluene and 97-98 wt % to 88 wt % of ethylene oxide and/or propylene oxide. The flexible foams described in EP-A 671425 contain only 33 g of chemically integrated diaminotoluene per cubic meter of foam.
GB-A 1398185 claims comparable polyols having 1-4 wt % of diaminotoluene and 96-99 wt % of alkylene oxides. The reported equivalent weights of 750-3500 g/mol are arithmetically equivalent to an OH number range of 16-75 mg KOH/g. These polyols are useful for producing flexible foams having densities of <30 kg/m3 and compressive strengths of 3.1-10.4 kg/m2.
U.S. Pat. No. 4,569,952 describes the use of from 8 to 25 wt % of low molecular weight diaminotoluene-based polyethers for producing very lightweight flexible foams having a density of 35-60 kg/m3 (2.14-3.79 lb./ft3).